For large-sized electrodes with a diameter of 700mm or more, what levels of tensile strength and elastic modulus should they reach in order to withstand extreme working conditions?

For large-size electrodes with a diameter of 700 mm or more, the indicators of flexural strength and elastic modulus need to be differentiated according to the electrode grade (regular power, high power, or ultra-high power) and the specific application scenario (such as large electric arc furnaces or submerged arc furnaces). For ultra-high power electrodes used in harsh working conditions, the flexural strength is usually required to reach above 10.0 MPa, while the elastic modulus needs to be controlled below 14.0 GPa, so as to improve thermal shock stability by utilizing a lower elastic modulus while ensuring mechanical load-bearing capacity.

Analysis of Core Indicators

Under extreme working conditions, flexural strength and elastic modulus are a pair of key parameters that need to be balanced. Flexural strength determines the electrode’s ability to resist fracture, while elastic modulus reflects the rigidity of the material. For large-size electrodes, an excessively high elastic modulus means the material is relatively brittle and prone to cracking when subjected to severe temperature changes.

Standards for ultra-high power electrodes: Industry standards (such as YB/T 4090) generally require that for ultra-high power electrodes of Φ550-Φ700 mm, the flexural strength should not be lower than 10.0-12.0 MPa, and the elastic modulus should not be higher than 14.0 GPa. Some enterprise standards for Φ650-Φ700 mm specifications control the flexural strength within the range of 10.0-13.0 MPa and tighten the elastic modulus to 7.0-10.0 GPa, so as to achieve better thermal shock resistance.

Specific Indicator Differences Among Electrodes of Different Grades

• Regular power electrodes: For extra-large regular power electrodes with a diameter of 700 mm to 960 mm, mainly used in submerged arc furnaces with low current density requirements, the flexural strength requirement for such electrodes is relatively low, usually ≥6.0 MPa, and the elastic modulus is controlled at ≤10.0 GPa. Their design logic tends to sacrifice part of the strength in exchange for better thermal shock stability, because the load fluctuations of submerged arc furnaces are relatively mild.
• High power and ultra-high power electrodes: With the increase in smelting intensity, electrodes need to withstand greater current and mechanical vibration. For mainstream ultra-high power electrodes in the specification range of Φ650-800 mm, the flexural strength is usually set at 8-15 MPa, and the elastic modulus is between 8-14 GPa. The lower limit of the elastic modulus of some high-end products can be about 7-9 GPa, which is achieved by optimizing the aggregate formula (such as increasing the proportion of needle coke) and the baking and impregnation process.

Selection Logic for Coping with Extreme Working Conditions

In direct current electric arc furnaces or high-power alternating current electric arc furnaces, electrodes not only bear the mechanical stress from their own weight and the holder, but also need to resist the thermal stress generated by arc impact and rapid cooling and heating. If the elastic modulus exceeds 14-16 GPa, even if the flexural strength meets the standard, the electrode is prone to cracking due to the inability to release internal stress during alternating cooling and heating. Therefore, the technical difficulty of large-size electrodes lies in how to reduce the elastic modulus as much as possible while ensuring sufficient strength.

For ultra-high power electrodes with a diameter exceeding 700 mm, the ideal balance point of indicators is usually to maintain the flexural strength in the medium-to-high range of 11-13 MPa, while suppressing the elastic modulus below 10 GPa (or even 7-9 GPa). Only in this way can structural integrity be maintained under the extreme thermal shock working conditions of large electric arc furnaces.